Known as “flying cigars” because of their sleek shapes, chimney swifts have come to rely almost totally on man-made structures like fireplace chimneys, airshafts and abandoned buildings for nesting sites and shelter. JIM MCCULLOUCH/CREATIVE COMMONS

Chimney swifts looking for suitable nesting sites

They are the chimney swifts, which have nested in our chimney in Decatur for the past several springs in a row. We don’t know if it’s the same pair from previous years or another pair, but, whatever, we’re glad to host them again.

Recently returned from their winter homes deep in the Amazon Basin in South America, the birds can be heard fluttering and twittering in the chimney now during the early evening, presumably building a nest. (Usually, a single chimney hosts only one pair of swifts)

The birds build a half-saucer shape nest from twigs and other plant material. Using saliva, they glue the material together and to the chimney wall. The female lays four to five whitish eggs, which hatch in about 21 days. The babies, which can be very noisy, fledge about a month after hatching.

Known as “flying cigars” because of their sleek shapes, chimney swifts now rely almost totally on man-made structures such as fireplace chimneys, air shafts and abandoned buildings for nesting and shelter. Deforestation and loss of large hollow trees have caused a scarcity of natural roosting and nesting sites.

But the birds can’t use just any chimney. Its inside walls must be made of stone, firebrick or masonry flue tiles with mortared joints, which allow the birds to cling to the walls — unlike the metal materials used in more modern homes.

Chimney swifts’ small but strong feet and four sharp gripping claws allow them to cling to rough vertical surfaces. Most other songbirds perch or stand upright.

The Atlanta Audubon Society encourages homeowners with suitable chimneys to provide temporary homes for the birds. A reward may be a less buggy yard — one chimney swift may eat 1,000 mosquito-sized insects per day.

Atlanta Audubon is building a 24-foot-tall “chimney swift tower” as part of a bird-friendly habitat that it’s creating in Piedmont Park. The tower will provide a nesting and roosting site for the swifts.

IN THE SKY: From David Dundee, Tellus Science Museum astronomer: The moon will be first quarter on Monday. Mercury is low in the east just before dawn. Brightly shining Venus is in the west at dusk and sets about two hours later. Mars and Saturn rise in the east around midnight. Jupiter is in the east at dusk.